Method of coating containers



May 12, 1942. J. SNADER ETAL METHOD OF COATING CONTAINERS Filed April 1,1939 Patented May 12, 1942 Ira J. Snader and James F. Earp, 3., Detroit,Mich, assignors to The American Paper Bottle Company, Toledo, Ohio, acorporation of Ohio Application April 1, 1939, Serial No.'265,522 I '9Claims. (01. 117-95) The present invention relates to methods of coatingcontainers, more particularly to methods of coating containers whichhave been fabricated of paper and are designed for use in the packagingof perishable products, especially milk and other food products whichmust of necessity be placed in sterile containers and maintained insterile condition until consumed.

The storage of liquids in containers fabricated of paper is rendereddifficult by reason of the absorbent nature of the fiber of which thepaper is made, paper readily absorbing liquids when brought into contacttherewith and becoming very weak when wet. It is therefore necessary toapply to the surfaces of a paper container to be used in the packagingof a liquid some coating substance which in and of itself is imperviousto liquid, or repels liquids, in order that the paper fibers of thecontainer may not become wet. It will be appreciated likewise that papercontainers made use of in the packaging and distribution of liquidsshould be of the self-supporting type and comparatively rigid, since thepressure of the liquid within the container is considerable even whenthe container is at rest, and the danger container is maintained in aheated atmosphere, erecting the container and introducing into itsinterior any additional small measured quantity of coating materialwhich may be necessary to insure full coverage of its bottom with suchmaterial, and subsequently chilling the coating material to effect itshardening. Coating of the containers in a nearly completed stage offabrication is advantageous in that the container need of failure is ofcourse increased when the .con-

tainer is handled or transported. Numerous materials may be employed ascoating substances for the walls of paper containers but that materialwhich has been most widely used comprises a paraflin or a parafilncontaining substance which not only resists penetration of liq uid whendeposited as a layer over the surface of a paper sheet but also impartsincreased stifiness to such sheet, thus increasing the ability of acontainer or the like, which comprises a plurality of such paper sheetsor panels, all coated, to maintain its shape during handling ortransportation, despite the internal pressure of the liquid andexternally applied blows or shocks incident to handling.

While the present invention contemplates a novel method of coating papercontainers of all forms and shapes with liquid coating compositionswhich are liquid at elevated temperatures and solid at roomtemperatures, it relates particularly to a method of coating containerswhich are of tubular form and substantially completed save for the finalclosure of one end, which end is only closed after the container hasbeen charged with the substance to be dispensed. Broadly speak-.

ing, the process comprises immersing the con-' tainer in a bath of themolten coating material, withdrawing the container from the bath anddraining off excess coating material while the be subjected to but fewfurther operations which tend to disturb the coating already applied.

Rractically all containers fabricated of paper include certain portionsof greater thickness than other portions. Ordinarily the bottom of acontainer of the tubular type comprises several plies or thicknesses ofpaper secured together by an adhesive whereas the side walls and top areof lighter construction. That portion of the container which is ofgreatest thickness tends to absorb more coating material than thoseportions of less thickness and likewiseis slower to cool after itstemperature has been raised .by immersion in a molten bath of coatingmaterial. In accordance with the present invention the aforementionedcharacteristics of the paper container are given full consideration and,afterthe container has been immersed, drained in a heated atmosphere,and erected, the heavier bottom of the container is covered with anadditional amount of coating material. Not only is this precaution takento ensure that an ample supply of the coating material covers the bottomof the freshly coated container, where of course leak age is most likelyto subsequently occur, but the cooling of the container is so efiectedthat practically all portions thereof are cooled simultaneously. Thisinvolves the withdrawal of a larger number of heat units from therelatively heavy (and heavily coated) bottom of the container in a givenperiod than from the relatively thin top or tubular body of thecontainer. This is accomplished by subjecting that portion of thecontainer which tends to retain heat longest to the action of a coolingmedium of higher heat conductivity than that portion of the container,or those portions, which are of lighter section.

For instance in the case of a tubular container with a multi-ply bottom,the heavier bottom portion of the freshly coated container is immersedin a liquid bath cooled to low temperature whereas the thinner portionsof the container wall are adequately cooled, and the coating materialthereon hardened, by the simple application A thereto of a current ofcooled air or other gas. It is highly advantageous to cool all portionsof a freshly coated container in this manner when the coating operationdescribed is carried out upon a complete automatic machine for thefabrication;-.coating, charging and sealing of paper containers, sincetime spentin effecting the cooling operation is minimized and themaximum speed of operation of the machine as a whole realized. y

The improved method will be hereinafter more fully described and in theaccompanying drawing, various instrumentalities for carrying out theseveral steps of the method are illustrated dia grammatically.

In the drawing:

Figure l is a view showing diagrammatically a portion of a mechanism bythe aid of which the immersion, draining and cooling of paper containersin accordance with the improved method, may be accomplished;

Figure 2 diagrammatically illustrates a means for directing cooled airor other gas over certain of the wall surfaces of a freshly coated con-'tainer;

Figure 3 is a fragmentary view showing portion of a means employed toefl'ect rocking movement of-a container to cause the small body ofcoating material resting upon the upper surface.

of its bottom to flow back and forth to effect proper distributionthereof;

Figure 4 is a vertical axial section through a paper container of a typeparticularly well adapted (to becoated by the improved coating process,an

Figure 5 shows the bottom portion of a container which has beenlaterally tilted. The container C, shown in section in Figure 4, issquare in horizontal section, having four side walls of similar area andshape: each comprising a single ply or thickness of paper. The bottomcomprises three plies of paper of the same thickness and the foldabletop C of the container is shown to be open. The paper employed ispreferably relatively light in weight but strong in texture and theresulting container is rigid and selfsupporting so long as its wallsremain dry. In order to prevent wetting and weakening of the containerwalls, the improved method which comprises the subject matter of thepresent application has been provided.

First the container is covered with the coatin material selected.Application of the coating material to the walls of the container may beeffected in various ways but this is preferably accomplished byimmersion since by immersing the container in a bath of the selectedcoating material in molten form, all areas of the same, both exteriorand interior surfaces, are brought into the chamber In through anaperture in its side wall such as indicated at l0, passing downwardlybottom end foremost, but with its major axis at an inclination to thevertical, entering the bath bottom end foremost, but still inclined,passing through the bath as shown, issuing fromthe bath bottom enduppermost so as to permit the coating material within the container todrain and finally reaching some position such as indicated at C being atthis point ready for removal from the chamber, all surfaces having beencoated but the excess coating liquid having been drained therefromduring its upward movement from the surface of the bath to position CThe mechanism employed for moving the containers through the bath andeffectingdraining thereof may vary as desired but we preferably make useof a mechanism such as that disclosed in our copending application,Serial 172,025. Thereafter the container is inverted, i. e., placedbottom end down by a mechanism such as that likewise disclosed in ourcopending application, the container coming to rest within a heatedchamber l2 closely adjacent the chamber III. At this point one or moredrops of molten coating material may be introduced into the open upperend of the container in order to ensure that the upper surface of thecontainer bottom is fully and adequately coated. As has previously beenpointed out, the relatively thick bottom of the container tends toabsorb more coating material than the side walls and it is obvious thatthere is a greater tendency for the container to leak spray device 13 ofany suitable form, positioned immediately above the container. The meansfor operating thenozzle I 3 may vary widely and comprises no part of thepresent invention. The coating material supplied, however, is preferablywithdrawn from the bath ll within the chamber Ill and forced upwardly tothe jet device l3 by a suitable pump.

After the introduction of a measured amount of additional coatingmaterial into a container full contact with the coating material. InFigure 1 of the drawing there is indicated at III a chamber for coatingmaterial and at I I a bath of coating material, for instance a paraillncontaining material, in the bottom of this chamber. It will beunderstood that suitable heating devices are utilized to maintainthebath of molten material in molten condition and to maintain theatmosphere in the chamber ll above the surface of the bath at arelatively high temperature so as to prevent solidification of themolten material upon any container so long as the container remains inthe chamber.

A plurality of containers are indicated at C, C', C, etc., and thesecontainers are intermittently or continuously advanced along apredetermined occupying position 0 the container is,pushed from thechamber 12 by a pusher (not. fllustrated) onto a steam heated trackwayl4 and at this point is loosely engaged by a conveying de-' vice (notillustrated) to be advanced along the trackway from left to right(Figure l). The

. trackway is illustrated in section in Figure 4. Its

details need not be described inasmuch as they are fully illustrated anddescribed in our copending application Serial 172,025. It is onlynecessary here to say that steam is circulated through the hollowinteriors of the two side rails II of the trackway so that these siderails are maintained in heated condition and prevent cooling of path inthe direction indicated by the arrows A,

the bottoms of containers which are dragged along the trackway.

The side rails II of the trackway are connected at spaced points bycross members I! and the rounded upper surfaces of the cross membersproject above the upper edges of the side rails l5; as indicated inFigure 3, so that containers passing along the trackway in the directionof the arrow B (Figure 1) will rock as their bottoms pass over theseveral cross members. This rocking movement of each container causesthe molten coating material which lies upon its bottom to flowrearwardly and forwardly across such oif with the containers.

no portion of the container bottom fails' to be subjected to contactwith coating material. Ultimately each successive container reaches aposition just without a housing diagrammatically indicated at H. In thenext operation of the conveyor it is brought within the housing and inFigure 1 of the drawing the containers indicated at C, C and on up to Care all within the housing [1.

Within this housing the cooling of the'container is effected and whenthe container is ultimately discharged from the housing it is quitecool, the coating material has entirely set, and the container is 'readyfor charging. The heated an adequate supply of trackway projects withinthe housing I6 for a certain distance, the containers in positions C, Cand C still resting upon the heated trackway. The container C however,has passed over the end of the heated trackway and dropped into a bath20 of liquid, for instance water, which has beencooled to a very lowtemperature, in the case of water almost to the point of freezing. Inthe usual case the empty paper container will be sufficiently buoyant toactually float on the bath 20 and will remain floating thereon until itsremoval from the bath by the action of the conveyor. The containeroccupying posi tion C has been moved the entire length of the bath 20and the next operation of the conveyor will effect its'removaltherefrom. The bath 20 is a relatively shallow body of fluid which iscontained. within a horizontally extending pan 2| supplied by means of aduct '22 with liquid at low temperature to replace that which passesDucts for refrigerant are indicated at 2| During the entire time thatthe containers are within the housing I! the upper portions thereof aresubjected to the action of cool gaseous currents, for instance currentsof cooled air, and in Figure 2 of the drawing the means for cir culatingthese cooled gaseous currents is dia-.

grammatically illustrated. It will be perceived that a battery of tubes25 are positioned within the housing It below the path of thecontainers. A fan, blower, or other air pumping mechanism, notillustrated, causes air to circulate through this battery of refrigerantcontaining tubes and to ,be thereby cooled, the upwardly flowing volumesof air being inwardly directed by vanes, such as indicated at 26, towardthe vertically disposed side walls of the line of containers passingthrough the housing, portion of the airflowing over the uppermost vane26 and striking a downwardly curved vane 21 by means of which a currentof air wilLbe caused to enter each container and to cool its interior.Vanes 28 direct cool air currents downwardly and inwardly against theopposite faces of the containers, entire stream or air current is drawndownwardly to a fan or; pump, to be recirculated, small and finally thei volumes of air being drawn into the casing I! to replace any whichescapes through its container inlet and discharge apertures. I

The specific means for causing currents of air to flow, first overcooling'means, and then over all inner'and outer surfaces of the sidewalls of the containers-may be widely varied, and likewise the detailsof the means employed for cooling the container bottoms by the use ofcooled liquids. In everykinstance, however, means will be employed thepurpose of which will be to eifect ,cooling of difierent portions of thecontainer by the utilization of fluids of different "that the coatingheat conducting capacities. The most'common fluids which may be usedare, of course, air and water. Any other suitable gases and liquids maybe employed, however, within the import of the invention.

It is sometimes considered desirable to cause the containers, as theypass along the trackway it toward the cooler H, to rock laterally of thetrackway as well as longitudinally thereof, to efi'ect a betterdistribution of the molten coating material over bottoms thereof. Thisis easily effected by tilting the trackway laterally, as shown in Figure5, at one or more points along its length. The trackway is flexible andmay be distorted by means of set screws such as indicated at I6 erallyfirst in one direction and then in the opposite direction. By thuslaterally and longitudinally tilting each container just after it hasreceived its added charge of coating material, such material will beefliciently distributed over the container bottom. After entering thecooling chamber l1 the containers are not rocked laterally, butlongitudinally of the trackway only.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. The method of coating containers with a substance which is liquid atelevated temperatures and solid at ordinary temperatures, whichcomprises applying such substance in liquid form .to the surfaces of acontainer in such manner that the coating layer is of difierentthicknesses over difierent areas of such surface, and cooling the coatedcontainer by subjecting the same to the action of a plurality of fluidcooling media of difl'erent heat conducting capacities, the areas ofgreater coatingthickness being brought into heat exchanging relationshipwith the cooling medium of greater heat conducting capacity and theareas of lesser coating thickness being brought into heat exchangingrelationship only with the cooling ing capacity.

2. The method of coating paper containers having portions of unequalthickness with a medium of lesser heat conductcoating substance which isliquid at elevated,

temperatures and solid at ordinary temperatures, comprising applyingsuch substance in liquid form to the surfaces of the container, andcooling the coated container by subjecting the same L. The method ofcoating containers with a substance which is liquid at elevatedtemperatures and solid at ordinary temperatures, which comprisesapplying such substance in liquid form to the surfaces of a container insuch manner layer is of different thicknesses over different areas ofsuch surface, and cooling the. more heavily coated portion of thecontainer by subjecting the same to the action of a liquid coolingmedium and subjecting, at the same time, the more lightly coated areasto the action of a gaseouscooling medium.

4. The method of coating paper containers hav-,

ing portions of unequal thickness with a coating tures and solid atordinary prising applying such substance in liquid form to the surfacesof the container, and cooling the to cause the'containersto rocklattions of the same to the action of a liquid cooling medium and agaseous cooling medium, and the lighter portions solely to the action ofa gaseo cooling medium.

5. The method of coating a paper container having a closed end orbottom, and an open end, which comprises immersing the container in abath of molten material which solidifies upon cooling, withdrawing anddraining the same, disposing the container with its open end uppermostand, while the coating remains fluid, introducing a supplementarymeasured body of liquid coating material into the interior thereof.

6. The method of coating a paper container having a flat closed end orbottom and an open end, which comprises dipping the container in a bathof molten material which solidifies upon cooling, draining the same,disposing the container with its open end uppermost, introducing asupplementary body of liquid coating material into the interior of thecontainer while the previously applied coating remains liquid, and rock-7 ing'the container to distribute the coating material over the bottomthereof.

7. The method set forth in claim 6 in which heat is applied to thecontainer bottom while the container is rocked and the container isdropped bottom end foremost into a cooling liquid immediately afterbeing rocked in the manner described.

8. The method set forth in claim 6 in which the container is rockedabout two horizontal axes which are angularly disposed to each other.

9. The method set forth in claim 6 in which the container is rockedwhileheat is imparted to the container bottom to prevent prematuresolidification of the coating material. a

IRA J; SNADER. JAMES F. EARP, JR.

